1. Field of the Invention
The present invention relates generally to a jointed stationary blade of a steam turbine and more particularly to a two stage jointed stationary blade, applicable to a high pressure or intermediate pressure steam turbine, in which an outer ring for jointing a front stage stationary blade and a rear stage stationary blade together fixedly is made in a bolt joint structure so as to be detached and disassembled easily thereby to have a reduced assembling man-hour and an enhanced maintainability.
2. Description of the Prior Art
In a high pressure or intermediate pressure steam turbine, trials are being performed using a two stage jointed stationary blade in which mutually adjacent front stage and rear stage stationary blades are fixedly jointed together. FIG. 4 is a cross sectional view of such a two stage jointed stationary blade after it has been assembled and FIGS. 5(a)-(b) are cross sectional views of two stationary blade structural portions before they are assembled. In particular, FIG. 5(a) shows a stationary blade (front stage) portion and FIG. 5(b) shows a stationary blade (rear stage) portion.
In the prior art two stage jointed stationary blade shown in FIG. 5, a stationary blade (front stage) 42 on an upstream side of steam flow S is constructed as in an integral structure fitted with an outer ring front portion 41 and an inner ring front portion 43 fixedly by welding. A stationary blade (rear stage) 52 is also constructed as in an integral structure fitted with an outer ring rear portion 51 and an inner ring rear portion 53 fixedly by welding. These integral stationary blades 42, 52 are jointed together fixedly by electron beam welding at a position, indicated by numeral 70 (FIG. 4), of the outer ring front portion 41 and the outer ring rear portion 51, such that the two stage jointed stationary blade is an integral structure.
It is to be noted that seal fitting portions 44, 54 are formed for fitting thereto labyrinth seals in the inner ring front portion 43 and the inner ring rear portion 53, respectively. Also, seal fin grooves 55, 56 are formed in the outer ring rear portion 51, as will be described later.
In the integral structure of the stationary blade (front stage) 42 shown in FIG. 5(a), the outer ring front portion 41 is fitted to an outer side of the blade via welded portions 45, 46 and the inner ring front portion 43 is fitted to an inner side of the blade via welded portions 47, 48. Also, the seal fitting portion 44 for fitting thereto a labyrinth seal is worked in the inner ring front portion 43.
In the integral structure of the stationary blade (rear stage) 52 shown in FIG. 5(b), the outer ring rear portion 51 consists of portions 51a, 51b, 51c. The portions 51a, 51b are jointed together via welded portions 58, 59 and the portions 51b, 51c are jointed together via welded portions 56, 57, and the outer ring rear portion 51 is fitted to an outer side of the blade via welded portions 57, 59. Also, the inner ring rear portion 53 is fitted to an inner side of the blade via welded portions 60, 61. The seal fitting portion 54 for fitting thereto a labyrinth seal is formed in the inner ring rear portion 53. Furthermore, the seal fin grooves 55, 56 are worked in the outer ring rear portion 51. Thus, the respective integral structures of the stationary blade (front stage) 42 and the stationary blade (rear stage) 52 are jointed together by electron beam welding at the position 70, as shown in FIG. 4, thereby the two stage jointed stationary blade is constructed.
In the prior art two stage jointed stationary blade as described above, the respective integral structures of the outer ring, the stationary blade and the inner ring are made by TIG (tungsten inert gas) welding or MAG (metal active gas) welding and the front stage and rear stage structural bodies thereof are jointed together by electron beam welding at the position of the outer ring front portion and rear portion, and thereby the two stage jointed stationary blade is made as an integral structure. Therefore, the front stage and rear stage portions thereof cannot be separated from each other for a repair or inspection work, which results in making the work difficult. Also, the welding work itself requires a lot of man-hours, especially the jointing of the outer ring front portion 41 and the outer ring rear portion 51 requires welding around an entire periphery of the outer ring. Thus, there is a problem that large facilities of jigs, tools, etc. for performing the welding operation are needed and the necessary man-hours is also increased.